The present invention relates to a vehicle lamp having a lamp body and a front lens which are integrally formed by blow molding into a lamp chamber as a hollow body lens unit. More particularly, the invention relates to a vehicle lamp whose lens portion in a body lens unit is provided with diffusion steps.
In order to decrease the number of component parts constituting a lamp, there has been known a conventional lamp which is constituted by integrally forming, by blow molding, a lamp body and a front lens. FIG. 13 shows a conventional license plate lamp, as an example, using a hollow body lens unit constructed by integrally forming a lamp body and a front lens by blow molding. More specifically, a bulb fitting hole 4 is provided in the lamp body portion 2 of a body lens unit 1 and a bulb 5 as a light source is fitted into the bulb fitting hole 4. Further, an emboss 3a having satin-like minute irregularities is formed on the outer surface of the lens portion 3 of the body lens unit 1 and the light emitted from the lens portion 3 is scattered so that a license plate 7 is irradiated therewith.
Since the emboss 3a is composed of minute irregularities, however, mud and dust resulting in lowering light distribution are apt to stick to the embossed surface and the problem is that even if it is attempted to sop up the mud and dust with a damp cloth and the like, the mud and dust adhering to the uneven surface are hardly easy to remove.
Although the formation of the emboss 3a on the inside of the lens portion 3 makes it unlikely that mud and dust stick to the embossed surface, forming the emboss 3a on the inside thereof is difficult because in the case of blow molding, the hollow body lens unit 1 is formed to a predetermined shape by supplying compressed air into a parison as a plastic material so as to elongate the plastic material by inflating the parison in such a way as to make the plastic material follow a molding surface.
In the case of a license plate lamp, moreover, the emboss 3a causes emitted light to remain to be only scattered, though a region where a difference in brightness occurs is desired to be minimized over the whole license plate 7. Consequently, though the quantity of plate-illuminating light is smoothed to some extent, a region 7a close to the light source of the license plate 7 is extremely bright, whereas a region 7b becomes dark by degrees as its distance from the light source increases. Thus, there develops a problem of deteriorating the visibility.
The present inventor has come to make the present invention by reasoning that a diffusion step is capable of positively controlling emission light and forming predetermined light distribution on the assumption that step elements lined up in a predetermined well-regulated direction gives the diffusion step a constant directivity and that mud and dust do not easily stick to the above diffusion step in comparison with the case of an emboss and even though the mud and dust come to stick thereto, the mud and dust can simply be wiped with a damp cloth and the like.
An object of the present invention based on the foregoing problems pertaining to the prior art and the present inventor""s reasoning is to provide a vehicle lamp whose lens portion has a diffusion step which is formed by blow molding on the outer surface of the lens portion and makes mud and dust not easily stick to the diffusion step and even though the mud and dust are caused to stick thereto, the mud and dust can simply be wiped with a dam cloth and the like.
In order to accomplish the object above, a vehicle lamp according to the present invention comprises a hollow body lens unit constructed by integrally forming a lamp body and a front lens which constitute a lamp chamber, a light source provided in the body lens unit, and a diffusion step such as a fish-eye step and a cylindrical step having step elements, each of which has constant directivity, the diffusion step being provided on the outer surface of lens portion of said body lens unit.
The diffusion step (the fish-eye step or cylindrical step) provided on the outer surface of the lens portion has the constant directivity as the step elements are lined up in the predetermined direction, and mud and dust are apt to slidably move in the direction of orientating the step, thus making the mud and dust not easily stick to the step elements.
Since mud and dust sticking to the diffusion step are apt to slidably move in the direction of orientating the step, moreover, the mud and dust can be wiped with a damp cloth and the like or washed off with flushing water in the direction of orientating the step.
Since the fish-eye step and the cylindrical step act in such a way as to positively diffuse the emitted light in the predetermined direction, it becomes easy to design light distribution in connection with deciding the quantity of light for illuminating a specific region in front of the lamp, to say nothing of uniformizing the quantity of light to be distributed.
According to another aspect of the present invention, the pitch width of each step element of the diffusion step is set not greater than twice the wall thickness of the lens portion.
If the pitch width of the step element is set greater than twice the wall thickness of the lens portion, not only the outer side in the step-forming area of the lens portion but also the inner side therein would follow the surface configuration of a blow mold at the time of blow molding. Consequently, the underside configuration of each step element is also to follow the front configuration of the step element, which results in lowering the light diffusing action. Therefore, the pitch width of each step element of the diffusion step has been set not greater than twice the wall thickness of the lens portion without making the inner side of the lens portion follow the surface configuration of the blow mold at the time of blow molding and also making the underside configuration of the step element follow the front configuration of the step element in order to make the underside thereof flat, so that the diffusion step performs a proper diffusing action.
According to still another aspect of the invention, the height of each step element of the diffusion step is set not greater than the wall thickness of the lens portion.
If the height of each step element of the diffusion step is set greater than the wall thickness of the lens portion, the step-forming area of the lens portion would expand outward (the inner side of the lens portion would cave in) at the time of blow molding and the strength of the lens portion may greatly be reduced because the branching portion between the step-forming area and a non-step-forming area in the lens portion becomes thin-walled in order to prevent not only the corresponding step-forming area on the inner side of the lens portion from extremely caving in at the time of blow molding but also the strength of the lens portion from weakening.
According to still another aspect of the invention, the vehicle lamp is a license plate lamp and the diffusion step is provided in an area at least directly opposite to the light source in the lens portion.
Although the quantity of light emitted from the lens portion is greatest in the area directly opposite to the light source, the light emitted from the area directly opposite to the light source of the lens portion is diffused by the diffusion step in the predetermined direction, whereby the light reaching the license plate lamp becomes smoothed.